On Mon, 16 Nov 2020 18:00:43 +0000, Roger Mills wrote:

The CurrentCost one http://www.currentcost.com/products.html

Is that showing true watts, or simply volt-amps by measuring the current
and multiplying it by nominal voltage without taking any account of
power factor?

It has no means of measuring the voltage unless there is a sneaky
means of getting that via a current transformer. When I last checked
what it was saying against the bills it was less than 1 kWHr out over
a days 20+ kWhr consumption.

None of these things are intended to be an accurate check meter just
a reasonable indicator of consumption. It could be scaled in bananas,
more bananas - bad, less bananas - good. B-)

I notice that there's also an optical version which counts
flashes from the meter - which should give true watt-hours. Does that
version have the same logging ability?

It's just an optical sensor and sender to the display unit. It's the
display unit that does the logging and history etc.

--
Cheers
Dave.